Lamination pack for skewed conductor bars and method of forming same

ABSTRACT

A lamination pack for a motor and method of forming the lamination pack is provided. The method includes inserting a plurality of conductor bars into a plurality of rotor slots defined by a lamination stack such that opposing bar ends of the conductor bars extend from opposing end faces of the lamination stack, skewing the lamination stack and the conductor bars to a skew angle relative to a rotation axis of the lamination stack, and subsequently bending the bar ends of the conductor bars in opposing radial directions to a locking angle greater than the skew angle, to lock each of the conductor bars in its respective rotor slot. The bent bar ends exert a compressive axial locking force on the lamination stack to prevent axial and radial movement of the laminations in the lamination stack and to prevent axial movement of the conductor bars relative to the lamination stack.

TECHNICAL FIELD

The disclosure relates to a lamination pack of a rotor, and a method offorming a lamination pack of a rotor.

BACKGROUND

Electromagnetic machines such as electric motors, generators, andtraction motors are useful for converting energy from one form toanother. Such electromagnetic machines often include an element such asa rotor which is rotatable about an axis. The rotatable element or rotormay be coaxial with a static element or stator, and energy may beconverted via relative rotation between the rotor and the stator.

One type of electromagnetic machine, an alternating current inductionmotor, uses induced current flow to magnetize portions of the rotorduring motor operation. More specifically, induced current may flowthrough conductor bars disposed nearly parallel to the axis along aperiphery of the rotor in a skewed configuration. The conductor bars areskewed relative to the axis along the periphery to reduce magneticlocking or cogging between the stator and rotor, to reduce magnetichumming noise during running condition, and to achieve uniform torque.Each conductor bar may be electrically connected to every otherconductor bar and/or by shorting elements disposed at opposite ends ofthe rotor. The shorting elements and conductor bars are subject toinertial forces during rotor operation.

SUMMARY

A method of forming a lamination pack of a rotor includes inserting aplurality of conductor bars into a plurality of rotor slots defined by alamination stack such that opposing bar ends of the conductor barsextend axially from opposing end faces of the lamination stack, andskewing the lamination stack and the conductor bars to a skew anglerelative to a rotation axis of the lamination stack, also referred toherein as the rotation axis of the lamination stack, to form a skewedlamination pack. A retaining force is applied to the skewed laminationpack to compress the laminations against each other, to prevent furtherradial rotation of each lamination relative to each other lamination inthe clamped skewed pack while exerting a bending force on the bar endsextending the opposing end faces of the skewed pack. While thelamination pack is clamped by the retaining force, the bending force isapplied to the bar ends to bend the respective bar ends of the conductorbars extending from the respective end faces of the skewed pack inopposing radial directions, where the bar ends are bent to a lockingangle which is greater than the skew angle, relative to the rotationaxis of the lamination pack, to lock each of the conductor bars in itsrespective rotor slot to prevent axial movement of the conductor barrelative to the lamination stack and such that the bent bar ends exert acompressive axial locking force on the lamination stack which preventsaxial and radial movement of the laminations in the locked and skewedlamination stack. Bending the bar ends to lock the bar ends of theconductor bars to the skewed lamination stack creates a lamination packwhich is advantaged by the prevailing compressive axial force exertedand maintained by the bent bar ends compressing the lamination stacksuch that the lamination pack resists high frequency vibration of theconductor bars in the stack during operation of the rotor in a motor andmaintains the density of the stack at a predetermined packing ratio todeliver consistent power density over time and resists cogging.

The method of forming a lamination pack includes providing a laminationstack to an apparatus configured to form the lamination pack. Thelamination stack defines a proximal face and a distal face spaced apartfrom the proximal face and further defines a longitudinal axis. Thelamination stack includes a plurality of laminations aligned radiallyrelative to the longitudinal axis such that the plurality of laminationsdefines a plurality of slots extending from the proximal face to thedistal face and distributed radially about a periphery of the laminationstack, and further includes a plurality of conductor bars. Eachconductor bar includes first and second bar ends and an intermediateportion intermediate the first and second bar ends. The intermediateportion of each conductor bar is disposed within a respective one of theplurality of slots such that the first bar end extends from the proximalface and the second bar end extends from the distal face. The methodincludes skewing the lamination stack including the conductor bars suchthat each of the plurality of conductor bars is skewed relative to thelongitudinal axis by a skew angle, then exerting a retaining force onthe skewed lamination stack, where the retaining force is sufficient toprevent axial movement and prevent radial rotation of each laminationrelative to each other lamination in the skewed lamination stack. Themethod continues with bending the first bar ends in a first radialdirection to a bend angle relative to the intermediate portion of theconductor bar and bending the second bar ends in a second radialdirection to the bend angle relative to the intermediate portion of theconductor bar, where the first radial direction opposes the secondradial direction. The retaining force is exerted on the lamination stackafter skewing the lamination stack and is maintained during bending ofthe first and second bar ends. After bending, the first and second barends exert a locking force on the lamination stack such that axial andradial movement of each lamination relative to each other lamination ofthe plurality of laminations is prevented.

In one example, the method includes positioning a first rotation platedefining a plurality of plate slots adjacent the proximal face, suchthat the first bar end of each of the plurality of conductor bars isreceived into a respective one of the plate slots of the first rotationplate, and positioning a second rotation plate defining a plurality ofplate slots adjacent the distal face, such that the second bar end ofeach of the plurality of conductor bars is received into a respectiveone of the plate slots of the second rotation plate. Each of the plateslots is defined by opposing support and contoured faces, where thecontoured face includes a skew face defining the skew angle and a bendface defining the bend angle. In this example, skewing the laminationstack includes rotating at least one of the first and second rotationplates by a first amount to exert a skewing force on the first andsecond bar ends via the interface between the first and second bar endsand the plate slots prior to exerting the retaining force, and bendingthe first and second bar ends includes rotating at least one of thefirst and second rotation plates by a second amount to exert a bendingforce on the first and second bar ends. The second amount of rotation isincremental to the first amount of rotation and the retaining force ismaintained during rotation of the at least one of the first and secondrotation plates by the second amount.

In another example, the method includes positioning a first shortingring defining a plurality of ring slots adjacent the proximal face, suchthat the first bar end of each of the plurality of conductor bars isreceived into a respective one of the ring slots of the first shortingring, and positioning a second shorting ring defining a plurality ofring slots adjacent the distal face, such that the second bar end ofeach of the plurality of conductor bars is received into a respectiveone of the ring slots of the second shorting ring. In this example,skewing the lamination stack prior to exerting the retaining forceincludes skewing the first shorting ring to the skew angle in the firstradial direction and skewing the second shorting ring to the skew anglein the second radial direction, where skewing the first and secondshorting rings to the skew angle exerts a skewing force on the first andsecond bar ends via the interface between the first and second bar endsand the ring slots. Bending the first and second bar ends, in thisexample, includes incrementally skewing the first shorting ring to alocking angle in the first radial direction and incrementally skewingthe second shorting ring to a locking angle in the second radialdirection, where the locking angle is equal to the sum of the skew angleand the bend angle. Incrementally skewing the first and second shortingrings to the locking angle exerts a bending force on the first andsecond bar ends via the interface between the first and second bar endsand the ring slots. The retaining force is maintained during incrementalskewing of the first and second shorting rings from the skew angle tothe locking angle. Each of the first and second shorting rings comprisesa plurality of shorting sheets, such that after bending, the first andsecond bar ends exert a locking force on the shorting sheets such thataxial and radial movement of each shorting sheet relative to each othershorting sheet of the plurality of shorting sheets is prevented. Theshorting sheets are made of an electrically conductive material, suchthat after bending, the shorting sheets in contact with the bent firstand second ends of the conductor bars electrically connect the conductorbars of the lamination pack to form a rotor.

As used herein, the terms “a,” “an,” “the,” “at least one,” and “one ormore” are interchangeable and indicate that at least one of an item ispresent. A plurality of such items may be present unless the contextclearly indicates otherwise. All numerical values of parameters,quantities, or conditions in this disclosure, including the appendedclaims, are to be understood as being modified in all instances by theterm “about” or “approximately” whether or not “about” or“approximately” actually appears before the numerical value. “About” and“approximately” indicate that the stated numerical value allows someslight imprecision (e.g., with some approach to exactness in the value;reasonably close to the value; nearly; essentially). If the imprecisionprovided by “about” or “approximately” is not otherwise understood withthis meaning, then “about” and “approximately” as used herein indicateat least variations that may arise from methods of measuring and usingsuch parameters. Further, the terminology “substantially” also refers toa slight imprecision of a condition (e.g., with some approach toexactness of the condition; approximately or reasonably close to thecondition; nearly; essentially). In addition, disclosed numerical rangesinclude disclosure of all values and further divided ranges within theentire range. Each value within a range and the endpoints of a range areall disclosed as separate embodiments. The terms “comprising,”“includes,” “including,” “has,” and “having” are inclusive and thereforespecify the presence of stated items, but do not preclude the presenceof other items. As used in this disclosure, the term “or” includes anyand all combinations of one or more of the listed items.

The above features and advantages and other features and advantages ofthe present disclosure will be readily apparent from the followingdetailed description of the preferred embodiments and best modes forcarrying out the present disclosure when taken in connection with theaccompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exploded perspective view of afirst apparatus for forming a lamination pack, showing the firstapparatus including first and second plates and a lamination packincluding a lamination stack and plurality of conductor bars;

FIG. 2 is a top view of the apparatus of FIG. 1;

FIG. 3 is a side perspective view of the apparatus of FIG. 1 showing thelamination pack prior to skewing the lamination stack and conductorbars;

FIG. 4 is a bottom view of the apparatus of FIG. 1;

FIG. 5 is a partial side view of the first rotation plate positioned onone end face of the lamination stack such that the plurality ofconductor bar ends extending from the one end face extend into the plateslots of the rotation plate;

FIG. 6 is a side view of one of the plate slots shown in FIG. 5;

FIG. 7 is a partial cross-sectional view of section 7-7 of FIG. 8Ashowing the clearance between the conductor bar and a lamination slot ofthe lamination stack of FIG. 1, prior to skewing the lamination stackand conductor bars;

FIG. 8A is a partial cross-sectional view of section 8-8 of FIG. 7,showing the conductor bar in the rotor slot prior to skewing thelamination stack and conductor bars;

FIG. 8B is the partial cross-sectional view of FIG. 8A after skewing thelamination stack and conductor bars and prior to bending the bar ends ofthe conductor bar;

FIG. 8C is the partial cross-sectional view of FIG. 8B after bending thebar ends of the conductor bar to a locking angle;

FIG. 9 is a schematic illustration of an exploded perspective view of asecond apparatus for forming a lamination pack including a laminationstack, a plurality of conductor bars and shorting rings, the apparatusshown in a side perspective view in FIG. 12 further including a rotatingtool;

FIG. 10 is a cross-sectional view of section 10-10 of the apparatus ofFIG. 12;

FIG. 11 is a partial bottom perspective view of the rotating tool of theapparatus of FIG. 10 including one of the shorting rings of thelamination pack of FIG. 9;

FIG. 12 is a side perspective view of the apparatus of FIG. 9 includingthe rotating tool of FIG. 11;

FIG. 13A is a partial cross-sectional view of section 13-13 of FIG. 10,showing the conductor bar in the rotor slot prior to skewing thelamination stack, the shorting ring, and the conductor bar;

FIG. 13B is the partial cross-sectional view of FIG. 13A after skewingthe lamination stack, the shorting ring, and the conductor bar;

FIG. 13C is the partial cross-sectional view of FIG. 13B after furtherskewing the shorting ring to bend the bar ends of the conductor bars toa locking angle to lock the lamination pack.

DETAILED DESCRIPTION

Referring to FIG. 1, a lamination pack is generally indicated at 10 andis shown in a first forming stage as a straight pack 10A. The laminationpack 10 and a method of forming the lamination pack 10 are describedherein. The lamination pack 10 may be useful as a component of a rotor(not shown), where the rotor may be useful as a component of anelectromagnetic machine (not shown) for automotive applications, e.g.,as a component of an alternating current induction motor for a vehicle(not shown). However, the lamination pack 10 may also be useful as acomponent of a rotor used for non-automotive applications, including useas a component of a generator or electric motor for residential andcommercial applications. Referring to the Figures, wherein likereference numerals refer to like elements, a lamination pack 10 isgenerally indicated at 10. During the various stages of forming thelamination pack 10, the lamination pack 10 is identified in the variousfigures and in the description as a straight pack 10A during a firststage of forming, as a skewed pack 10B during a second stage of forming,and as locked pack 10C during a third stage of forming, where the first,second and third stages of forming are performed sequentially. Forexample, the lamination pack 10 is shown as a straight pack 10A in FIGS.1, 8A and 13A, where a bar axis 11 of each of the conductor bars 12 isaligned with the rotation axis 13. The lamination pack 10 is shown as askewed pack 10B in a second forming stage in FIGS. 8B and 13B, and as alocked pack 10C in a third forming stage in FIGS. 8C and 13C. The methodof forming the lamination pack 10 uses, in a first embodiment shown inFIGS. 1 through 8C, a first apparatus generally indicated at 14 in FIG.1 including first and second rotation plates. In a second embodimentshown in FIGS. 9-13C, the method of forming the lamination pack 10 usesa second apparatus generally indicated at 16 in FIG. 9 including arotation tool 17 and fixture 18. The elements shown in FIGS. 1-13C arenot necessarily to scale or proportion. Accordingly, the particulardimensions and applications provided in the drawings presented hereinare not to be considered limiting.

Generally, and referring to the partial sectional views shown in FIGS.8A-8C and 13A-13C, the method of forming the lamination pack 10generally includes forming a straight pack 10A, skewing the straightpack 10A to form a skewed pack 10B, then bending the ends of theconductor bars 12 extending from the skewed pack 10B to form a lockedpack 10C. The straight pack 10A, which is shown in FIGS. 1 and 9, isformed by inserting a plurality of conductor bars 12 into a plurality ofrotor slots 19 defined by a lamination stack 20 such that opposing barends 21 of the conductor bars 12 extend axially from opposing proximaland distal end faces 23, 24 of the lamination stack 20 and such that thelongitudinal bar axis 11 of each bar 12 is parallel to the longitudinalrotation axis 13 of the lamination stack 20. The skewed pack 10B isformed by skewing the lamination stack 20 and the conductor bars 12 ofthe straight pack 10A to a skew angle θ relative to a rotation axis 13of the lamination stack 20. A clamping force is applied to thelamination stack 20 of the skewed pack 10B to retain the relativeposition of the laminations 22 and the conductor bars 12 in the skewedconfiguration during forming of a locked pack 10C. While maintaining theclamping force, the respective proximal and distal bar ends 21 of theconductor bars 12 are bent to a bend angle Φ relative to the bar axis11, e.g., the bar ends 21 are bent to a locking angle (θ+Φ) relative tothe rotation axis 13, where the locking angle (θ+Φ) is defined by theskew angle θ and the bend angle Φ and is in the same radial direction asand greater than the skew angle θ. As shown in FIG. 8C, the distal barends 21 are bent in a first radial direction, and the proximal bar ends21 are bent in a second radial direction opposing the first radialdirection, such that the distal and radial bar ends 21 of each conductorbar 12 are bent in opposing radial directions such that each of thedistal and radial bar ends 21 exerts an axial compressive force on arespective distal and radial face of the skewed lamination stack 20,thereby forming the locked pack 10C and exerting an axial compressivelocking force on the skewed lamination stack 20 to prevent axial andradial movement of the laminations 22 relative to each other and toprevent axial and radial movement of each conductor bar 12 in itsrespective rotor slot 19. Bending the bar ends 21 to lock the bar ends21 and conductor bars 12 to the skewed lamination stack 20 creates alocked pack 10C which is advantaged by the prevailing compressive axiallocking force exerted and maintained by the bent bar ends 21 compressingthe lamination stack 20 such that the lamination pack 10 resists highfrequency vibration of the conductor bars 12 in the stack 20 duringoperation of a rotor including the lamination pack 10 in a motor, andmaintains the density of the stack 20 at a predetermined packing ratiosuch that the rotor including the lamination pack 10 delivers consistentand relatively high power density over time and resists cogging.

Referring to FIG. 1, in a first embodiment, the lamination pack 10 isshown in a first forming stage as a straight pack 10A provided to theapparatus 14. The apparatus 14 is operable to skew the straight pack 10Ato form the skewed pack 10B, to compress the lamination stack 20 afterskewing and prior to bending the bar ends 21, and to bend eachrespective bar end 21 relative to an intermediate portion 29 of eachrespective bar to form the locked pack 10C. The straight pack 10Aprovided to the apparatus 14 includes a lamination stack generallyindicated at 20 and a plurality of conductor bars 12, where each of thebars 12 is inserted through a respective rotor slot 19 of a plurality ofrotor slots 19 defined by the lamination stack 20. The lamination stack20 has opposing end faces spaced apart from each other and referred toherein as a proximal face 23 and a distal face 24. The lamination stack20 defines a bore 25 therethrough extending from the proximal face 23 tothe distal face 24. The bore 25 defines a rotation axis 13 of thelamination pack 10 and is configured to receive a rotor shaft. In use ina rotor, the rotor including the lamination pack 10 rotates on the rotorshaft such that in use the rotation axis 13 of the bore 25 issubstantially coincident with the axis of the rotor shaft. The rotorslots 19 defined by the lamination stack 20 are distributed radiallyabout a periphery 26 of the lamination stack 20, each rotor slot 19extending from the proximal face 23 to the distal face 24. Thelamination stack 20 includes a plurality of laminations 22 stackedadjacent to each other. Each lamination 22 defines a center hole 27 anda plurality of lamination slots 28 distributed radially about aperiphery 26 of the lamination 22. In the example shown, each lamination22 is a steel lamination 22 consisting of an individual annular layerof, for example, silicon steel. In the partially formed condition shownin FIG. 1, the straight pack 10A includes the lamination stack 20 havingthe laminations 22 stacked adjacent each other to define the bore 25,where the laminations 22 are radially aligned relative to each othersuch that the lamination 22 slots are aligned in the lamination stack 20to define the plurality of rotor slots 19. Each of the rotor slots 19extends the axial length of the straight pack 10A such that each rotorslot 19 of the straight pack 10A is substantially parallel to therotation axis 13.

As shown in FIG. 7, each lamination slot 28 is configured to receive aconductor bar 12 to form the straight pack 10A including a plurality ofconductor bars 12. By way of non-limiting example, the straight pack 10Amay include from about 30 to about 100 conductor bars 12 spaced aboutthe axis of rotation. Each conductor bar 12 may be configured to conductelectrical current during operation of an electromagnetic machine (notshown) including the lamination pack 10, and each conductor bar 12 maytherefore be formed from an electrically-conductive material. Forexample, each conductor bar 12 may be formed from copper or a copperalloy, such as a copper nickel alloy or a copper boron alloy. In anotherexample, each conductor bar 12 may be formed from aluminum or analuminum alloy. Each of the conductor bars 12 includes an intermediateportion 29 disposed between opposing first and second bar ends 21. Eachof the conductor bars 12 is inserted into a respective rotor slot 19 ofthe lamination stack 20, such that the intermediate portion 29 of theconductor bar 12 is disposed within the rotor slot 19 and such that thefirst bar end 21 extends from the proximal face 23 of the laminationstack 20 and the second bar end 21 extends from the distal face 24 ofthe lamination stack 20, as shown in FIG. 1. As referred to herein, thebar axis 11 of the conductor bar 12 is defined by the intermediateportion 29 of the bar 12.

The laminations 22 may be stacked and the conductor bars 12 may beinserted in the lamination stack 20 by any suitable means to provide thestraight pack 10A shown in FIG. 1. By way of non-limiting example, eachsteel lamination 22 may be individually stamped and then subsequentlystacked and pressed adjacent another steel lamination 22 using a mandrel30 to form the lamination stack 20. By way of non-limiting example, theconductor bars 12 may be manually inserted into the rotor slot 19 byhand, or each conductor bar 12 may be inserted into a respective rotorslot 19 by an automated process or machine. The process of inserting theconductor bars 12 into the rotor slots 19 may further include aligningthe conductor bars 12 relative to each other such that the length towhich each of the first bar ends 21 extends from the proximal face 23 ofthe lamination stack 20 is substantially the same, and the length towhich each of the second bar ends 21 extends from the proximal face 23of the lamination stack 20 is substantially the same. In one example,the straight pack 10A may be assembled and then retained on the mandrel30, which may be a mandrel such as the mandrel 30 shown in the apparatus14 of FIG. 1, such that the straight pack 10A may be assembled on themandrel 30 and retained on the mandrel 30 by a retainer 31 to form amandrel assembly 32. The mandrel assembly 32 including the mandrel 30,the retainer 31, and the straight pack 10A may then be provided to theapparatus 14,16 for subsequent forming of the straight pack 10A into thelamination pack 10 as further described herein.

In a first non-limiting example shown in FIG. 1, the mandrel 30 includesa shank 33 configured to receive the straight pack 10A, and/or toreceive the individual laminations 22, where the laminations 22 arestacked on the mandrel 30 to form the lamination stack 20 and/or thestraight pack 10A. The shank 33 may be characterized by a shank 33diameter which allows for slip fit of the center hole 27 of thelaminations 22 and/or the bore 25 of the lamination stack 20 to theshank 33, such that the shank 33 diameter may be marginally smaller thanthe diameter of the bore 25. The mandrel 30 includes a head 34 defininga clamp face 35 configured such that when the lamination stack 20 ispositioned on the mandrel 30, the proximal face 23 of the laminationstack 20 is adjacent the clamp face 35 and in contact with the clampface 35.

The mandrel 30 is configured to be adjustably fastened to the retainer31 after the straight pack 10A is received onto the mandrel 30, to formthe mandrel assembly 32. In the illustrative example shown in FIG. 1,the mandrel 30 includes a fastening interface 36 which in the example isa threaded stud 36. The stud 36 may be adjustably fastened to fasteninginterface 37 of the retainer 31, which in the example is a threaded hole37 in the retainer 31. The retainer 31 defines a retainer face 38configured such that when the lamination stack 20 is positioned on themandrel 30 and the retainer 31 is fastened to the mandrel 30, the distalface 24 of the lamination stack 20 is adjacent the retainer face 38 andin contact with the retainer face 38. The position of the retainer face38 relative to the clamp face 35, e.g., the axial distance between theretainer face 38 and the clamp face 35, may be adjusted by adjusting theposition of the retainer 31 relative to the head 34 by adjusting thethreaded connection between the stud 36 and the threaded hole 37. In theexample shown in FIG. 1, the mandrel 30 includes an adjustment interface39 configured in the example as a hex drive 39. The adjustment interface39 is adjustable to exert a torque on the mandrel 30 to change the axiallength between the retainer face 38 and the clamp face 35 by adjustmentof the threaded connection, to change a compressive clamping forceexerted by the retainer 31 and the head 34 of the mandrel 30 on thelamination stack 20 via the retainer face 38 in contact with the distalface 24 of the lamination stack 20 and the clamp face 35 in contact withthe proximal face 23 of the lamination stack 20. It would be understoodthat the clamping force exerted on the lamination stack 20 would beproportional to the torque input to the adjustment interface 39, suchthat the torque input to the adjustment interface 39 could be controlledto control the magnitude of the clamping force exerted by the clamp face35 and retainer face 38 on the lamination stack 20.

For example, during forming of the lamination stack 20, the laminations22 may be positioned on the shank 33 of the mandrel 30 and retained tothe mandrel 30 by the retainer 31 fastened to the mandrel 30 with theretainer 31 adjusted such that the retainer 31 and the head 34, viarespectively, the retainer face 38 and the clamping face 35, cooperateto exert a compressive clamping force on the lamination stack 20. Themagnitude of the clamping force exerted on the lamination stack 20 maybe adjusted via the threaded connection to exert an “aligning force,”where the term “aligning force,” as used herein, refers to a clampingforce of a magnitude which is sufficient to hold the laminations 22 inaxial contact with each other, e.g., to minimize or prevent axialmovement of the laminations 22, however still allow radial rotation ofeach lamination 22 relative to adjacent laminations 22 in the laminationstack 20, such that the laminations 22 can be rotated radially relativeto each other to “align” the lamination slots 28 to define the pluralityof rotor slots 19, and such that the plurality of rotor slots 19 can bealigned in a predetermined orientation to the rotation axis 13 and toeach other. After alignment of the lamination slots 28, the retainer 31may be further tightened to the lamination stack 20 by adjusting thethreaded connection to decrease the axial distance between the retainerface 38 and the clamp face 35, to exert a “retaining force” on thelamination stack 20, where the term “retaining force” as used hereinrefers to a clamping force of a magnitude which is sufficient to preventaxial movement and prevent radial rotation of the laminations 22relative to each other, to “retain” both the axial and radial alignmentof each of the laminations 22 relative to adjacent laminations 22 in thelamination stack 20.

In the present example, the straight pack 10A is formed by receiving thelamination stack 20 on the mandrel 30, exerting an aligning force toorient the laminations 22 axially adjacent to each other, and, whilemaintaining the aligning force on the lamination stack 20, rotating thelaminations 22 relative to each other to align the lamination slots 28to form the rotor slots 19, such that the rotor slots 19 aresubstantially parallel to each other and parallel to the rotation axis13. The aligning force is maintained during insertion of a conductor bar12 into each of the rotor slots 19, to form the straight pack 10A shownin FIG. 1, including the conductor bars 12 and lamination stack 20,where each of the conductor bars 12 and each of the rotor slots 19 aresubstantially parallel to each other and parallel to the rotation axis13. The lamination stack 20 may be retained on the mandrel 30 clamped inthis manner for transfer of the mandrel assembly 32 including thestraight pack 10A to the forming operations shown in FIGS. 1 and 9.

Referring to FIG. 7, a cross-sectional view of the conductor bar 12disposed within the rotor slot 19 of the straight pack 10A is shown. Asshown in FIG. 7, the thickness T of the conductor bar 12 may vary alongthe radial length of the conductor bar 12. In the example shown in FIG.7, the conductor bar 12 defines a tapered portion that tapers radiallyfrom a thickness T₁ to a thickness of T₂. In the example shown, theconductor bar 12 further includes an axial tab 40 extending the axiallength of the intermediate portion 29. As shown in FIG. 7, each of thelamination slots 28 forming the rotor slot 19 is contoured to thecross-sectional shape of the conductor bar 12, and to provide aclearance gap x between the rotor slot 19 and the conductor bar 12 alongthe radial length A of the conductor bar 12. In the example shown, theclearance gap x is of a constant width along the tapered portion of theconductor bar 12 between T₁ and T₂. The lamination slot 28 defines a tabslot which opens to the periphery 26 of the lamination stack 20 toreceive the tab 40 during insertion of the conductor bar 12 to the rotorslot. The tab slot is configured to provide a clearance gap x+Δx betweenthe tab 40 and the tab slot, where x+Δx is greater than x. In oneexample, Δx=0.005 mm. The clearance gaps x and x+Δx allow for insertionof the conductor bar 12 through the lamination slot 28. Further, thewidth x of the clearance gap is configured such that after skewing ofthe straight pack 10A shown in partial view in FIG. 8A to form theskewed pack 10B shown in partial view in FIG. 8B, the clearance gap xbetween the conductor bar 12 and each lamination slot 28 is closed asshown in FIG. 8B, such that the opposing sides of the conductor bar 12are each in contact with the adjacent surfaces of the lamination 22defining the lamination slot 28, and such that the interference betweenthe skewed laminations 22 and skewed conductor bar 12 constrains axialand radial movement of the conductor bar 12 in the skewed pack 10B.

Referring to FIGS. 1-4, a first embodiment of an apparatus 14 isgenerally indicated at 14 and is operable to form the lamination pack10. The apparatus 14 includes a first rotation plate 41 and a secondrotation plate 42. Each of the first and second rotation plates 41, 42defines an inboard surface 43 configured to interface with and be incontact with a respective end face 22, 23 of the straight pack 10A whenthe straight pack 10A is positioned in the apparatus 14 as shown inFIGS. 2-4, such that in this position each of the inboard surfaces 43 isoriented axially inboard relative to the lamination pack 10. Each of thefirst and second rotation plates 41, 42 includes a central opening 44which is of sufficient size to receive the head 34 of the mandrel 30and/or the retainer 31. In the example shown, the opening 44 of at leastone of the rotation plates 41, 42 has a diameter which is slightlylarger than the diameter of the head 34, such that the head 34 hasclearance to pass through and/or be received into the opening 44, andthe opening 44 of at least the other of the rotation plates 41, 42 has adiameter which is slightly larger than the diameter of the retainer 31,such that the retainer 31 has clearance to pass through and/or bereceived into the opening 44.

Each of the rotation plates 41, 42 defines a plurality of plate teeth 45which are distributed radially about the periphery 46 of the plates 41,42 to define a plurality of plate slots 47, where the plate slots 47 arearranged to receive the plurality of bar ends 21 extending from endfaces 23, 24 of the straight pack 10A, as shown in FIG. 1. As shown inFIGS. 2-4, in a first stage of forming, the straight pack 10A ispositioned in the apparatus 14 such that the inboard surface 43 of thefirst rotation plate 41 is adjacent to and interfaces with the proximalface 23 of the straight pack 10A, and the head 34 of the mandrel 30 isreceived into the opening 44 of the first rotation plate 41. Each of theplurality of bar ends 21 extending from the proximal face 23 is receivedinto a respective one of the plurality of plate slots 47 defined by thefirst rotation plate 41. The second rotation plate 42 is positioned onthe straight pack 10A opposing the first rotation plate 41 such that theinboard surface 43 of the second rotation plate 42 is adjacent to andinterfaces with the distal face 24 of the straight pack 10A, and theretainer 31 is received into the opening 44 of the second rotation plate42. Each of the plurality of bar ends 21 extending from the distal face24 is received into a respective one of the plurality of plate slots 47defined by the second rotation plate 42. During this first stage offorming, which comprises positioning the rotation plates 41, 42 atopposing ends of the straight pack 10A, the rotation plates 41, 42 arealigned to each other such that each of the conductor bars 12 and rotorslots 19 of the straight pack 10A is parallel to the rotation axis 13,as shown in FIG. 8A in a representative side view showing one of theconductor bars 12 disposed in a rotor slot 19 during the first stage offorming.

During the second stage of forming the lamination pack 10, the rotationelements 48,49 are rotated in opposing radial directions by apredetermined skew angle θ to form the skewed pack 10B. In the exampleshown in FIGS. 1-4, the first rotation plate 41 includes a firstrotation element 48 and the second rotation plate 42 includes a secondrotation element 49, where the first and second rotation elements 48,49are rotatable to rotate the first and second plates 41, 42 in opposingdirections when affixed to the straight pack 10A, to skew the conductorbars 12 relative to the rotation axis 13 by contact of the plate teeth45 with the bar ends 21 during rotation of the plates 41, 42. Skewing ofthe conductor bars 12 displaces the laminations 22 radially relative toeach other, as shown in FIG. 8B, to form the skewed pack 10B, where eachof the conductor bars 12 are skewed relative to the rotation axis 13 bythe skew angle Θ. After skewing the straight pack 10A shown in FIG. 8Ato form the skewed pack 10B shown in FIG. 8B, the mandrel 30 andretainer 31 of the mandrel assembly 59 are adjusted to exert a retainingforce on the skewed pack 10B, thereby preventing both axial and radialmovement of each lamination 22 relative to each other lamination 22 inthe skewed pack 10B.

During a third stage of forming the lamination pack 10, and whileexerting the retaining force on the skewed pack 10B to prevent axial andradial movement of the laminations 22 in the skewed pack 10B, therotation elements 48,49 are incrementally rotated in opposing radialdirections 51,52 by a predetermined amount, for example, by apredetermined number of degrees, to exert a bending force on the barends 21 extending from the proximal and distal end faces 23, 24 of thelamination stack 20, to bend each respective bar end 21 relative to theintermediate portions 29 of the respective bar 12 and relative to thebar axis 11 of the respective bar 12 by a bend angle Φ, to lock each ofthe bar ends 21 to the lamination stack 20, thus forming the locked pack10C. The bar ends 21 bent in opposing directions at the opposing endfaces 23, 24 of the lamination stack 20 exert an axial compressivelocking force on the lamination stack 20, as shown in FIG. 8C, to formthe locked pack 10C. The “locking force”, as that term is used herein,refers to the axial compressive force exerted by the opposing bent barends 21 of each conductor bar on the skewed lamination stack 20, e.g.,on the locked pack 10C shown in FIG. 8C. The “locking force”collectively exerted on the skewed lamination stack 20 by the opposingbent bar ends 21 of the plurality of bent conductor bars 12 issufficient to prevent both axial and radial movement of the laminations22 in the lamination stack 20 and to prevent both axial and radialmovement of the conductor bars 12 relative to the rotation axis 13before and after removal of the mandrel 30 and retainer 31 from thelocked pack 10C, thus forming the locked pack 10C shown in part in FIG.8C.

In the illustrative example shown in FIGS. 1-4, the first rotationelement 48 is configured as a hexagonal element 48 having a plurality ofpairs of opposing flats 50, such that the first rotation element 48 canreceive and be rotated by a driver (not shown) compatible with at leastone of the pairs of opposing flats 50 to rotate the first rotation plate41 relative to the rotation axis 13. In one example, the second rotationelement 49 is configured as a truncated cylinder defining a pair ofopposing flats 50, such that the second rotation element 49 can receivea driver compatible with the pair of opposing flats 50. In one example,the drivers are attachable respectively to the first and second rotationelements 48,49 and rotatable in opposing directions to rotate the firstand second plates 41, 42 in opposing directions, where the direction ofrotation of the first rotation plate 41 relative to the second rotationplate 42 is indicated by arrow 51 in FIG. 3 and the direction ofrotation of the second rotation plate 42 relative to the first rotationplate 41 is indicated by arrow 52 in FIG. 3.

Each of the first and second plates 41, 42 defines a plurality of plateslots 47 shown in detail in FIGS. 5 and 6. Each plate slot 47 is definedby a pair of immediately adjacent plate teeth 45A, 45B. As shown indetail in FIGS. 6 and 7, the plate slot 47 is defined on one side by asupport face 53 of a plate tooth 45A and on the other side by acontoured face 54 of an immediately adjacent plate tooth 45B. Thesupport face 53 is configured to support the bar end 21 during thesecond stage of forming, e.g., during skewing of the straight pack 10Ato form the skewed pack 10B shown in partial view in FIG. 8B, and tosupport the bar end 21 during the third stage of forming, e.g., duringbending of the opposing bar ends 21 to form the locked pack 10C shown inpartial view in FIG. 8C. In the example shown, the support face isgenerally planar and parallel to the rotation axis 13. The contouredface 54 includes a skew face 55 extending an axial length L1 of theplate and a bend face 56 extending an axial length L2 of the plate,where the bend face 56 is disposed intermediate the skew face 55 and theinboard surface 43 of the plate. The axial lengths L1 and L2 are relatedby the equation:L1=2(L2)  (1)such that L1 is two-thirds the length of the tooth 45, e.g.,L1=⅔(L1+L2).

The skew face 55 is defined by a skew angle θ which is equivalent to theskew angle θ of the conductor bars 12 of the skewed pack 10B, shown inpartial sectional view in FIG. 8B, where the skew angle θ is relative tothe rotation axis 13. The skew angle θ may be defined by the operatingand/or performance requirements of the rotor including the laminationpack 10. The bend face 56 is defined by a bend angle Φ which is the bendangle Φ by which the bar ends 21 of each conductor bar is bent relativeto the intermediate portion 29 of the respective bar 12 and relative tothe bar axis 11 defined by the respective intermediate portion 29, shownin partial sectional view in FIG. 8C. As shown in FIG. 8C, the bar end21 extending from the proximal face 23 of the lamination stack 20 isbent by the bend angle Φ in the direction indicated by arrow 51, and theopposing bar end 21 of the same conductor bar extending from the distalface 24 of the lamination stack 20 is bent by the bend angle Φ in theopposing direction indicated by arrow 52. The bend angle Φ is relativeto the skew angle θ, such that the bent bar ends 21 of the locked pack10C shown in FIG. 8C are bent to a locking angle defined as (θ+Φ)relative to the rotation axis 13. The bend angle Φ is determined suchthat the bar ends 21 extending from the respective end faces 23, 24 ofthe skewed pack 10B, when bent to the bend angle Φ while exerting theretaining force on the skewed pack 10B to form the locked pack 10C,compress the lamination stack 20 to a specified load defining thelamination stack 20 packing ratio. The specified load exerted by thebent bar ends 21 on the skewed lamination stack 20 of the locked pack10C is also referred to herein as the locking force. After removing theretaining force, for example, by removing the mandrel 30 and retainer 31from the locked pack 10C, the bent bar ends 21 continue to exert thelocking force such that the locked pack 10C maintains the definedlamination stack packing ratio. In one example, the bending angle Φ isapproximately two degrees (2°) and the skew angle θ is approximately sixdegrees (6°) such that the locking angle (θ+Φ) is approximately eightdegrees (8°) relative to the rotation axis 13. In one example, the skewangle θ is 6.43°, the bend angle Φ is 2°, and the locking angle (θ+Φ) of8.43°.

In the example shown in FIG. 6, the plate slot 47 is characterized by aslot width W, where:W=T+C  (2)and where T is the radial thickness T of the conductor bar 12, and C isa clearance between the conductor bar 12 and the plate slot 47 where theskew face 55 terminates at an outboard surface 57 of the plates 41, 42as shown in FIG. 6. The width W of the plate slot 47 is equal to thethickness T of the bar plus the clearance C to allow for twist duringskewing of the straight pack 10A to form the skewed pack 10B, such thatthe bar follows the curvature of the helix of the rotor slots 19 of thelamination stack 20. The width W allows for twisting of the bar whenforming the skewed pack 10B, without pinching the bar ends 21. The widthW allows sufficient clearance such that the rotation plates 41, 42 canbe removed from the bend pack 10C after bending of the bar ends 21 tothe bend angle Φ. The twist for the bar across the width W of the bar isestimated by the equation:

$\begin{matrix}{{Twist} = {\frac{1}{m} - \sqrt{\left( \frac{1}{m} \right)^{2} - \left( \frac{L}{2} \right)^{2}}}} & (3)\end{matrix}$where:L=L1+L2  (4)and m is defined by the equation:

$\begin{matrix}{m = \frac{\left( \frac{L}{\theta} \right)}{(R)^{2} - \left( \frac{L}{\theta} \right)^{2}}} & (5)\end{matrix}$where R is the radius of the lamination. The clearance C is defined bythe equation:C=((Twist)×(L1+L2)/L)−T  (6)where T, as described previously, is the radial thickness of theconductor bar. As shown in FIG. 7, the width W of the plate slot 47varies as the thickness T of the bar varies along the radial length ofthe bar, for example, from T1 to T2.

FIGS. 8A, 8B and 8C show a partial section of the lamination pack 10 ateach stage of forming, and are illustrative of a method of forming alamination pack 10 using the apparatus 14 shown in FIGS. 1-4. FIG. 8Ashows the straight pack 10A which may be assembled on a mandrel 30 (asshown in FIGS. 1-4), where in the first stage of forming the laminationpack 10, the laminations 22 are stacked such that each rotor slot 19defined by the lamination stack 20 is substantially parallel to therotation axis 13, and each conductor bar 12 is inserted in eachrespective rotor slot 19 is substantially parallel to the rotation axis13. The straight pack 10A may be retained on the mandrel 30 by aretainer 31 adjusted to exert an aligning force on the lamination stack20 to maintain axial alignment of the laminations 22 relative to eachother, while allowing radial rotation of each lamination relative to theother laminations 22 in the lamination stack 20.

As shown in FIGS. 1-4, during the second stage of forming the laminationpack 10, a first rotation plate 41 is positioned on the proximal face 23of the straight pack 10A such that the proximal bar ends 21 are receivedinto the plate slots 47 of the first rotation plate 41. The secondrotation plate 42 is positioned on the distal face 24 of the straightpack 10A such that the distal bar ends 21 are received into the plateslots 47 of the first rotation plate 41. As received, each bar end 21 ispositioned in a respective plate slot 47 such that the bar end 21 issubstantially parallel to the support face 53. As the rotation plates41, 42 are rotated in opposing radial directions as shown by arrows51,52, the skew face 55 of each respective plate slot 47 contacts thebar end 21 and exerts a skewing force to skew the conductor bars 12 andlaminations 22 to the skew angle as shown in FIG. 8B, to form the skewedpack 10B shown in FIG. 8B.

After forming the skewed pack 10B, the retainer 31 and mandrel 30 areadjusted, e.g., tightened, to increase the clamping force exerted on thelamination stack 20 from an aligning force to a retaining force, wherethe retaining force is sufficient to prevent both radial and axialmovement of the laminations 22 in the skewed pack 10B. The mandrel 30and retainer 31 may be adjusted to exert a retaining force that achievesa predetermined and/or minimum packing density of the lamination stack20, to remove and/or minimize entrapped air in the lamination stack 20.

In the third forming step, and while the mandrel 30 and retainer 31maintain a retaining clamping force on the skewed pack 10B, the rotationplates 41, 42 are incrementally rotated in opposing radial directions asshown by the arrows 51,52, such that the bend face 56 of each respectiveplate slot 47 contacts the bar end 21 and exerts a bending force on therespective bar end 21. The bending force exerted on each respective barend 21 is resisted by the intermediate portion 29 of the respective bardisposed in a respective rotor slot 19 of the skewed pack 10B, where theskewed laminations 22 are retained in the skewed position by theretaining force exerted by the mandrel assembly 32, such that thebending force acts on the bar ends 21 to bend the bar ends 21 to thebend angle Φ relative to the intermediate portion 29 of each bar 12,where the bend angle Φ originates at a bend point at the interface ofthe bar end 21 and the respective one of the end faces 23, 24 from whichthe bar 12 end is extending, as shown in FIG. 8C. The bar ends 21 bentin opposing directions at the opposing end faces 23, 24 of thelamination stack 20 exert an axial compressive locking force on thelamination stack 20, as shown in FIG. 8C, to form the locked pack 10C.The “locking force”, as that term is used herein, refers to the axialcompressive force exerted by the opposing bent bar ends 21 of eachconductor bar on the skewed lamination stack 20. The “locking force”collectively exerted on the skewed lamination stack 20 by the opposingbent bar ends 21 of the plurality of bent conductor bars 12 issufficient to prevent both axial and radial movement of the laminations22 in the lamination stack 20 and to prevent both axial and radialmovement of the conductor bars 12 relative to the rotation axis 13before and after removal of the mandrel 30 and retainer 31 from thelocked pack 10C, thus forming the locked pack 10C shown in part in FIG.8C. In one example, the locking force exerted by the bent bar ends 21 issufficient to achieve a predetermined minimum packing ratio of thelamination 22 pack 10C and to prevent axial and radial movement of theconductor bars 12 and laminations 22, such that the locked pack 10C isadvantaged by being resistant to high frequency vibration of theconductor bars 12 in the stack 20 during operation, for example in amotor, of a rotor including the lamination pack 10. The locking forceexerted by the bent bar ends 21 is maintained over a useful lifetime ofthe lamination pack 10, thereby maintaining the density of the stack 20at the predetermined packing ratio over time, such that the rotorincluding the lamination pack 10 delivers consistent and relatively highpower density over time and is resistant to cogging.

After forming the locked pack 10C, the locked pack 10C may be furtherprocessed to form a rotor including the locked pack 10C, for example, byshorting together the bar ends 21 extending from the distal face 24 ofthe lamination stack 20 to electrically connect the distal bar ends 21,and shorting together the bar ends 21 extending from proximal face 23 ofthe lamination stack 20 to electrically connect the proximal bar ends21, to form the rotor, such that electrical current can be conductedthrough the electrically connected (shorted) plurality of conductor bars12. By way of non-limiting example, the bar ends 21 may be welded orsoldered together to electrically connect the conductor bars 12. Inanother example, first and second end rings may be formed separately,and then subsequently welded, brazed, or soldered onto the respectivefirst and second plurality of bar ends 21 extending respectively fromthe proximal and distal faces 23, 24 of the lamination stack 20. Inanother example, an end ring may be overcast onto each respective endface 23, 24 of the locked pack 10C, where the overcast end ring is madefrom an electrically conductive metal such as, by way of non-limitingexample, copper, a copper alloy, aluminum, or an aluminum alloy, toelectrically connect the plurality of bar ends 21 extending from therespective end face 23, 24. In other non-limiting examples, the end ringmay be pressure cast, gravity cast, or die cast over the plurality ofbar ends 21 extending from each end face 23, 24 of the locked pack 10C.

Referring to FIGS. 9-13, another illustrative example of a method andapparatus 16 for forming a lamination pack 10 including the locked pack10C is shown. In this embodiment, an end ring 60 defining a plurality ofring slots 68 distributed radially about the periphery 46 of the endring 60 is positioned adjacent each of the distal face 24 and theproximal face 23 of the straight pack 10A, such that each of theplurality of bar ends 21 extending from the respective end face 23, 24is received into a respective one of the plurality of ring slots 68defined by the end ring 60, and such that, in the locked pack 10C shownin FIG. 13C, each of the bar ends 21 is electrically connected to theend ring 60. The end ring 60 is formed of a plurality of stackedshorting sheets 61, as further described herein, and may be referred toherein as a shorting ring. The straight pack 10A may be formed aspreviously described for FIG. 1, such that the straight pack 10Aincludes a lamination stack 20 consisting of a plurality of stackedlaminations 22 defining a plurality of rotor slots 19. Each of aplurality of conductor bars 12 is inserted into a respective one of theplurality of rotor slots 19 such that a first bar end 21 of each barextends from the proximal face 23 of the lamination stack 20 and asecond bar end 21 of each bar extends from the distal face 24 of thelamination stack 20, with the intermediate portion 29 of each bar 12contained within the rotor slot. As described for FIG. 1, the straightpack 10A may be assembled on a mandrel, which by way of non-limitingexample may be one of the mandrels 30 shown in the mandrel assemblies32, 59 shown in FIGS. 1 and 9. In FIGS. 9 and 10 a mandrel assembly 59including a mandrel 30, a retainer 31, and fastening elements 58 forfastening the retainer 31 to the mandrel 30 is shown. In one example,the straight pack 10A may be assembled on the mandrel 30 and retained onthe mandrel 30 by the retainer 31 and fastening elements 58, to form amandrel assembly 59. The mandrel assembly 59 including the mandrel 30,the retainer 31, the fastening elements 58, and the straight pack 10Amay then be provided to the apparatus 16 for subsequent forming of thestraight pack 10A into the lamination pack 10 as further describedherein.

In the non-limiting example shown in FIGS. 9 and 10, the mandrel 30includes a shank 33 and a head 34 defining a clamp face 35, as describedrelated to FIG. 1 and configured such that when the lamination stack 20is positioned on the mandrel 30, the proximal face 23 of the laminationstack 20 is adjacent the clamp face 35 and in contact with the clampface 35. The mandrel 30 shown in FIGS. 9-10 is configured to beadjustably fastened to the retainer 31 after the straight pack 10A isreceived onto the mandrel 30, to form the mandrel assembly 59. Themandrel 30 includes fastening interfaces 36, which in the illustrativeexample shown in FIGS. 9-10 are configured as blind holes which arethreaded to engage the threaded interfaces 37 of the fastening elements58. The retainer 31 may be adjustably fastened to the mandrel 30 by thefastening elements 58, where the threaded interface 37 of each fasteningelement 58 is received into a respective fastening interface 39 of theretainer 31, shown in the present example as a threaded through hole 39,and engages the fastening interface 36 of the mandrel 30. The retainer31 defines a retainer face 38 configured such that when the laminationstack 20 is positioned on the mandrel 30 and the retainer 31 is fastenedto the mandrel 30, the distal face 24 of the lamination stack 20 isadjacent the retainer face 38 and in contact with the retainer face 38.The position of the retainer face 38 relative to the clamp face 35,e.g., the axial distance between the retainer face 38 and the clamp face35, may be adjusted by adjusting the position of the retainer 31relative to the head 34 by adjusting the threaded connection between thethreaded interfaces 37 of the fastening elements 58, the threadedinterfaces 39 of the retainer 31, and the fastening interfaces 36 of themandrel 30. For example, the fastening elements 58 may be tightened orloosened relative to the mandrel 30 to change the compressive clampingforce exerted by the retainer 31 and the head 34 of the mandrel 30 onthe lamination stack 20 via the retainer face 38 in contact with thedistal face 24 of the lamination stack 20 and the clamp face 35 incontact with the proximal face 23 of the lamination stack 20. It wouldbe understood that the clamping force exerted on the lamination stack 20would be proportional to the torque input to the fastening elements 58,such that the torque input to the fastening elements 58 could becontrolled to control the magnitude of the clamping force exerted by theclamp face 35 and the retainer face 38 on the lamination stack 20.

As described for FIG. 1, during forming of the lamination stack 20, thelaminations 22 may be positioned on the shank 33 of the mandrel 30 andretained to the mandrel 30 by the retainer 31 fastened to the mandrel 30with the retainer 31 adjusted such that the retainer 31 and the head 34,via respectively, the retainer face 38 and the clamping face 35,cooperate to exert a compressive clamping force on the lamination stack20. The magnitude of the clamping force exerted on the lamination stack20 may be adjusted via the threaded connection established by thefastening elements 58 in threaded engagement with the retainer 31 andthe mandrel 30 to exert an aligning force. As previously described, theterm “aligning force” refers to a clamping force of a magnitude which issufficient to hold the laminations 22 in axial contact with each other,e.g., to minimize or prevent axial movement of the laminations 22,however still allow radial rotation of each lamination 22 relative toadjacent laminations 22 in the lamination stack 20, such that thelaminations 22 can be rotated radially relative to each other to “align”the lamination slots 28 to define the plurality of rotor slots 19, andsuch that the plurality of rotor slots 19 can be aligned in apredetermined orientation to the rotation axis 13 and to each other.After alignment of the lamination slots 28, the retainer 31 may befurther tightened to the lamination stack 20 by adjusting the threadedconnection established by the fastening elements 58 in threadedengagement with the retainer 31 and the mandrel 30 to decrease the axialdistance between the retainer face 38 and the clamp face 35, to exert aretaining force on the lamination stack 20, where the term “retainingforce” as used herein refers to a clamping force of a magnitude which issufficient to prevent axial movement and prevent radial rotation of thelaminations 22 relative to each other, to “retain” both the axial andradial alignment of each of the laminations 22 relative to adjacentlaminations 22 in the lamination stack 20.

FIGS. 9-12 show the apparatus generally indicated at 16. The apparatus16 includes a rotation tool generally indicated at 17 and a rotationfixture generally indicated at 18. Each of the rotation tool 17 and therotation fixture 18 defines a rotation element 64 having an inboardsurface 43 configured to interface with and be in contact with an endface 23, 24 of the straight pack 10A when the straight pack 10A anddistal and proximal shorting rings 60 are positioned between therotation tool 17 and rotation fixture 18 of the apparatus 16, and therotation element 64 of each of the rotation tool 17 and the rotationfixture 18 is received into a respective central aperture 15 of arespective one of the shorting rings 60, as illustrated by FIGS. 9-12.When positioned as shown in FIGS. 10-11, each of the inboard surfaces 43of the rotation elements 64 of the rotation tool 17 and the rotationfixture 18 is oriented axially inboard relative to the lamination pack10. The central aperture 15 defines a first rotation interface 62, whichin the non-limiting example shown in FIGS. 9-11 is configured as aplurality of keyways 62 which are distributed radially about the centralaperture 15. By way of example, the central aperture 15 may also bereferred to herein as a keyed aperture 15. Each rotation element 64defines a second rotation interface 63 corresponding to the firstrotation interface 62. The non-limiting example shown in FIGS. 9-11 isconfigured as a plurality of keys 63 which are distributed radiallyabout the rotation element 64 to correspond to the keyways 62, such thatthe keyed rotation element 64 can be fitted to and received into thecentral aperture 15 and the keyways 62 of the shorting ring 60. Each ofthe rotation tool 17 and the rotation fixture 18 includes a centralopening 44 which is of sufficient size to receive the head 34 of themandrel 30 and/or the retainer 31. In the example shown, the opening 44of at least one of the rotation tool 17 and rotation fixture 18 has adiameter which is slightly larger than the diameter of the head 34, suchthat the head 34 has clearance to pass through and/or be received intothe opening 44, and the opening 44 of at least the other of the rotationtool 17 and rotation fixture 18 has a diameter which is slightly largerthan the diameter of the retainer 31, such that the retainer 31 hasclearance to pass through and/or be received into the opening 44.

Referring to FIGS. 9 and 11, each of the shorting rings 60 positioned onthe distal and proximal end faces 23, 24 of the straight pack 10Ainclude a plurality of shorting sheets 61 which are stacked and alignedto form the shorting ring 60. In the example shown, each shorting sheet61 defines a plurality of sheet slots 67 distributed radially about theperiphery of the shorting sheet 61 such that when the shorting sheets 61are stacked and aligned, the aligned sheet slots 67 define the ringslots 68 of the shorting ring 60. Each shorting sheet 61 consists of anindividual annular layer of an electrically conductive material, such ascopper or aluminum, such that when the shorting ring 60 is operativelyconnected to the conductor bar ends 21, the shorting ring 60 isoperative as an end ring, e.g., the shorting ring 60 electricallyconnects the plurality of connector bars 12 such that electrical currentcan be conducted through the electrically connected plurality ofconductor bars 12, and such that the lamination pack 10 and the shortingrings 60 form a rotor.

Each shorting ring 60 includes a central aperture 15 which defines afirst rotation interface 62 adapted to receive a second correspondinginterface 63 defined by the rotation element 64. In the non-limitingexample shown, the central aperture 15 is a keyed aperture defining afirst corresponding keyway 62. The second corresponding interface 63defined by the rotation element 64 is configured as a key 63 which canbe received into the keyway 62, to exert a rotation force on theshorting ring 60 via the keyway 62. As shown in FIGS. 9-11, the keyedrotation element 64 defines a plurality of keys 63 distributed radiallyabout the periphery of the rotation element 64. The keyed aperture 15includes a plurality of keyways 62 distributed radially about thecircumference of the keyed aperture 15, such that each keyway 62 isarranged to receive a respective key 63 of the rotation element 64. Asshown in FIGS. 9-12, each of the rotation tool 17 and the rotationfixture 18 includes a keyed rotation element 64. In the example shown,one shorting ring 60, which may be referred to herein as a distalshorting ring 60, is positioned on the rotation fixture 18 such that thekeys 63 of the keyed rotation element 64 of the rotation fixture 18 arereceived into the keyways 62 of keyed aperture 15 of the distal shortingring 60, to align the shorting sheets 61 forming the distal shortingring 60. The bar ends 21 extending from the distal face 24 of thestraight pack 10A are received into the ring slots 68 of the distalshorting ring 60, to position the straight pack 10A on the rotationfixture 18, as shown in FIG. 10. Another shorting ring 60, which may bereferred to herein as a proximal shorting ring 60, is positioned on theproximal face 23 of the straight pack 10A, such that the bar ends 21extending from the proximal face 23 of the straight pack 10A arereceived into the ring slots 68 of the proximal shorting ring 60, wherethe shorting sheets 61 of the proximal shorting ring 60 are aligned todefine the plurality of keyways 62. The keyed rotation element 64 of therotation tool 17 can be operatively attached to the proximal shortingring 60 by inserting the keys 63 of the rotation element 64 into therespective keyways 62 defined by the proximal shorting ring 60. Inanother example, as shown in FIG. 11, the proximal shorting ring 60 canfirst be formed by stacking the shorting sheets 61 on the rotationelement 64 of the rotation tool 17, and the proximal shorting ring 60and rotation tool 17 can be concurrently placed on the proximal end ofthe straight pack 10A such that the bar ends 21 extending from theproximal face 23 are received into the ring slots 68 of the proximalshorting ring 60. The example of corresponding interfaces defined by thekeyways 62 and the keys 63 is non-limiting, and other configurations ofcorresponding interfaces 62,63 may be used to operatively connect arotation element 64 to the shorting ring 60, such that the rotationelement 64 can be rotated to exert a skewing force on the shortingsheets 61.

In a first forming step, using the apparatus 16 shown in FIGS. 9-12, astraight pack 10A is provided to the apparatus 16. After assembling thedistal and proximal shorting rings 60 to the mandrel assembly 59including the straight pack 10A, and operatively attaching the rotationfixture 18 and the rotation tool 17, respectively, to the distal andproximal shorting rings 60, as shown FIGS. 10 and 11, the rotation tool17 is rotatable, in a second forming step, in a radial direction 51 torotate the rotation element 64 positioned in the keyed aperture 15 ofthe proximal shorting ring 60, and the rotation element 64 of therotation fixture 18 exerts a resistive radial force on the distalshorting ring 60, to skew the straight pack 10A and the shorting sheets61 of the distal and proximal shorting rings 60 to the skew angle θ, asshown in FIG. 13B, to form the skewed pack 10B. Skewing of the conductorbars 12 displaces the laminations 22 and the shorting sheets 61 radiallyrelative to each other, as shown in FIG. 13B, to form the skewed pack10B, where each of the conductor bars 12 are skewed relative to therotation axis 13 by the skew angle Θ. After skewing the straight pack10A shown in FIG. 13A to form the skewed pack 10B shown in FIG. 13B, themandrel 30, retainer 31 and fastening elements 58 of the mandrelassembly 59 are adjusted to exert a retaining force on the skewed pack10B, thereby preventing both axial and radial movement of eachlamination 22 relative to each other lamination 22 in the skewed pack10B. As shown in FIG. 10, the clamp face 35 of the mandrel 30 is indirect contact with the proximal face 23 of the skewed pack 10B and theretainer face 38 of the retainer 31 is in direct contact with the distalface 24 of the skewed pack 10B, such that after exerting the retainingforce on the skewed pack 10B, the shorting sheets 61 of each shortingrings 60 are not subjected to the retaining force, e.g., the shortingsheets 61 are radially adjustable relative to each other by furtherrotation of the rotation tool 17.

During a third stage of forming the lamination pack 10, and whileexerting the retaining force on the skewed pack 10B to prevent axial andradial movement of the laminations 22 in the skewed pack 10B, therotation tool 17 including the rotation element 64 is incrementallyrotated in the radial direction 51 by a predetermined amount, forexample, by a predetermined number of degrees, to exert an incrementalskewing force on shorting sheets 61 of each of the shorting rings 60,such that the shorting rings 60 exert a bending force on the bar ends 21extending from the proximal and distal end faces 23, 24 of thelamination stack 20, to bend each respective bar end 21 relative to theintermediate portions 29 of the respective bar and relative to the baraxis 11 of the respective bar by a bend angle Φ, to lock each of the barends 21 to the lamination stack 20, thus forming the locked pack 10Cshown in FIG. 13C. The bar ends 21 bent in opposing directions at theopposing end faces 23, 24 of the lamination stack 20 exert an axialcompressive locking force on the lamination stack 20, as shown in FIG.8C, to form the locked pack 10C. The “locking force”, as that term isused herein, refers to the axial compressive force exerted by theopposing bent bar ends 21 of each conductor bar 12 on the skewedlamination stack 20. The “locking force” collectively exerted on theskewed lamination stack 20 by the opposing bent bar ends 21 of theplurality of bent conductor bars 12 is sufficient to prevent both axialand radial movement of the laminations 22 in the lamination stack 20 andto prevent both axial and radial movement of the conductor bars 12relative to the rotation axis 13 before and after removal of the mandrel30 and retainer 31 from the locked pack 10C, thus forming the lockedpack 10C shown in part in FIG. 13C. The rotation element 64 is removablefrom the keyed aperture 15 after formation of the locked pack 10C. Thebent bar ends 21 exert the locking force on the shorting rings 60, thuslocking the shorting sheets 61 of the shorting rings 60 to the lockedpack 10C, as shown in FIG. 13C, and preventing both axial and radialmovement of the locked shorting sheets 61 relative to the rotation axis13 before and after removal of the rotation element 64 from the keyedaperture 15 of each of the distal and proximal shorting rings 60. Asshown in FIG. 13C, the incrementally skewed shorting rings 60 have beenskewed to the skew angle θ and incrementally skewed by the bend angle Φsuch that each of the shorting sheets 61 is skewed by the locking angle(θ+Φ), when locked as shown in FIG. 13C. Each of the shorting sheets 61is locked in contact with each conductor bar. The shorting sheets 61 aremade from an electrically conductive material such that the shortingsheets 61 in contact with the bend bar ends 21 provide electricallyconductive paths between the bar ends 21, such that electrical currentcan be conducted through the electrically connected plurality ofconductor bars 12 to form a rotor including the locked pack 10C andshorting sheets 61 shown in FIG. 13C.

The “locking force” collectively exerted on the skewed lamination stack20 and incrementally skewed shorting rings 60 by the opposing bent barends 21 of the plurality of bent conductor bars 12 is sufficient toprevent both axial and radial movement of the laminations 22 in thelamination stack 20, to prevent both axial and radial movement of theshorting sheets 61 in the shorting rings 60, and to prevent both axialand radial movement of the conductor bars 12 relative to the rotationaxis 13 before and after removal of the mandrel 30, the retainer 31, andthe rotation elements 64 from the locked pack 10C, thus forming thelocked pack 10C shown in part in FIG. 13C. In one example, the lockingforce exerted by the bent bar ends 21 is sufficient to achieve apredetermined minimum packing ratio of the shorting rings 60 and lockedpack 10C, and to prevent axial and radial movement of the conductor bars12, laminations 22 and shorting sheets 61, such that the locked pack 10Cshown in FIG. 13C is advantaged by being resistant to high frequencyvibration of the conductor bars 12 in the stack 20 during operation, forexample in a motor, of a rotor formed of the lamination pack 10including the locked pack 10C and distal and proximal shorting rings 60.The locking force exerted by the bent bar ends 21 is maintained over auseful lifetime of the lamination pack 10, thereby maintaining thedensity of the shorting rings 60 and stack 20 at the predeterminedpacking ratio over time, such that the rotor including the locked pack10C and distal and proximal shorting rings 60 delivers consistent andrelatively high power density over time and is resistant to cogging.

The example apparatus and methods disclosed herein are not intended tobe limiting, and it would be understood that various alternatives forforming the lamination pack 10 and/or a rotor containing the laminationpack 10 can be used. By way of non-limiting example, at least a portionof the method for forming the lamination pack 10 may automated and/orexecuted with the use of robots or other automation. For example, theembodiment illustrated by FIGS. 1-8C may be executed using an automatedprocess which includes the mandrel 14 and the first end plate 41 locatedin a fixture or device configured to receive the lamination stack 20.The lamination stack 20 can be manipulated after being received onto themandrel 14 to align the lamination slots 28 to form the rotor slots 19and to align the slots 19 with the plate slots 47, for example, using arobot or automated alignment device, such as one or more alignmentfingers inserted to one or more respective rotor slots 19. The conductorbars 12 can be inserted automatically to the rotor slots 19 as thelamination stack 20 is retained in an aligned orientation on the mandrel14 and relative to the fixture plate 41, to insert each conductor bar 12through a respective rotor slot 19 and into a respective plate slot 47.The lamination pack 10 and/or conductor bars 12 may be vibrated by thedevice during insertion to ensure the conductor bars 12 are fullyreceived into the plate slots 47.

After inserting the conductor bars 12, the second end plate 42 can bepositioned on the lamination stack 20 such that the bar ends 21extending from the lamination stack 20 are received into the plate slots47 of the second end plate 42. The second end plate 42 may beautomatically positioned on the lamination stack 20, for example, by arobot, and the retainer 31 applied to the mandrel 14 to exert thealigning force, prior to automatically rotating at least one of thefirst and second end plates 41, 42 to skew the lamination stack 20 andconductor bars 12 to the skew angle, to form the skewed pack 10B. Theretainer 31 may be automatically adjusted to increase the compressiveforce exerted on the skewed pack 10B from the aligning force to aretaining force, prior to automatically rotating at least one of thefirst and second end plates 41, 42 to bend the bar ends 21 to the bendangle, to lock the conductor bars 12 to the lamination stack 20 and formthe locked pack 10C. The retaining force is released from the lockedpack 10C, for example, by removal of the retainer 31, and the mandrel 14and end plates 41, 42 automatically removed from the locked pack 10C.The locked pack 10C may be automatically, e.g., robotically, transferredto a subsequent operation to form electrical connections between thebent bar ends 21. For example, the locked pack 10C can be roboticallyinserted into a casting die for casting of cast end rings toelectrically connect the bent bar ends 21. Likewise, the embodimentillustrated by FIGS. 9-13C may be executed using a process which is atleast partially automated and/or robotized.

While the best modes for carrying out the disclosure have been describedin detail, those familiar with the art to which this disclosure relateswill recognize various alternative designs and embodiments forpracticing the disclosure within the scope of the appended claims.

The invention claimed is:
 1. A method of forming a lamination pack, themethod comprising: providing a lamination stack, wherein the laminationstack: defines a proximal face and a distal face spaced apart from theproximal face; defines a longitudinal axis; includes a plurality oflaminations aligned radially relative to the longitudinal axis such thatthe plurality of laminations defines a plurality of slots extending fromthe proximal face to the distal face and distributed radially about aperiphery of the lamination stack; includes a plurality of conductorbars, wherein: each conductor bar includes first and second bar ends andan intermediate portion intermediate the first and second bar ends; andthe intermediate portion of each conductor bar is disposed within arespective one of the plurality of slots such that the first bar endextends from the proximal face and the second bar end extends from thedistal face; skewing the lamination stack including the conductor barssuch that each of the plurality of conductor bars is skewed relative tothe longitudinal axis by a skew angle; exerting a retaining force on thelamination stack; wherein the retaining force prevents axial movementand prevents radial rotation of each lamination relative to each otherlamination; bending the first bar ends in a first radial direction to abend angle relative to the intermediate portion of the conductor bar;bending the second bar ends in a second radial direction to the bendangle relative to the intermediate portion of the conductor bar; whereinthe first radial direction opposes the second radial direction; whereinthe retaining force is exerted on the lamination stack after skewing thelamination stack and is maintained during bending of the first andsecond bar ends; and wherein after bending, the first and second barends exert a locking force on the lamination stack such that axial andradial movement of each lamination relative to each other lamination ofthe plurality of laminations is prevented.
 2. The method of claim 1,wherein the first and second bar ends are bent concurrently.
 3. Themethod of claim 1, wherein providing the lamination stack furthercomprises: receiving the lamination stack onto a mandrel; afterreceiving the lamination stack onto the mandrel, attaching an adjustableretainer to the mandrel; the method further comprising: after skewingthe lamination stack, adjusting the retainer to exert the retainingforce on the skewed lamination stack.
 4. The method of claim 3, wherein:the mandrel defines a clamping face; the retainer defines a retainerface; and the clamping face interfaces with one of the proximal face andthe distal face, and the retainer face interfaces with the other of theproximal face and the distal face such that the retaining force isexerted on the skewed lamination stack via the clamping face and theretainer face.
 5. The method of claim 1, wherein exerting the retainingforce on the lamination stack includes compressing the lamination stackto a predetermined packing ratio.
 6. The method of claim 1, furthercomprising: positioning a first rotation plate defining a plurality ofplate slots adjacent the proximal face, such that the first bar end ofeach of the plurality of conductor bars is received into a respectiveone of the plate slots of the first rotation plate; positioning a secondrotation plate defining a plurality of plate slots adjacent the distalface, such that the second bar end of each of the plurality of conductorbars is received into a respective one of the plate slots of the secondrotation plate; wherein skewing the lamination stack includes rotatingat least one of the first and second rotation plates by a first amountto exert a skewing force on the first and second bar ends via theinterface between the first and second bar ends and the plate slotsprior to exerting the retaining force; wherein bending the first andsecond bar ends includes rotating at least one of the first and secondrotation plates by a second amount to exert a bending force on the firstand second bar ends; and wherein the second amount of rotation isincremental to the first amount of rotation and the retaining force ismaintained during rotation of the at least one of the first and secondrotation plates by the second amount.
 7. The method of claim 6, wherein:each of the plate slots is defined by opposing support and contouredfaces; and the contoured face includes a skew face defining the skewangle and a bend face defining the bend angle.
 8. The method of claim 1,further comprising: positioning a first shorting ring defining aplurality of ring slots adjacent the proximal face, such that the firstbar end of each of the plurality of conductor bars is received into arespective one of the ring slots of the first shorting ring; positioninga second shorting ring defining a plurality of ring slots adjacent thedistal face, such that the second bar end of each of the plurality ofconductor bars is received into a respective one of the ring slots ofthe second shorting ring; wherein skewing the lamination stack prior toexerting the retaining force includes: skewing the first shorting ringto the skew angle in the first radial direction; and skewing the secondshorting ring to the skew angle in the second radial direction; whereinskewing the first and second shorting rings to the skew angle exerts askewing force on the first and second bar ends via the interface betweenthe first and second bar ends and the ring slots; wherein bending thefirst and second bar ends includes: incrementally skewing the firstshorting ring to a locking angle in the first radial direction; andincrementally skewing the second shorting ring to a locking angle in thesecond radial direction; wherein: the locking angle is equal to the sumof the skew angle and the bend angle; incrementally skewing the firstand second shorting rings to the locking angle exerts a bending force onthe first and second bar ends via the interface between the first andsecond bar ends and the ring slots; and the retaining force ismaintained during incremental skewing of the first and second shortingrings from the skew angle to the locking angle.
 9. The method of claim8, wherein each of the first and second shorting rings comprises aplurality of shorting sheets.
 10. The method of claim 9, wherein afterbending, the first and second bar ends exert a locking force on theshorting sheets such that axial and radial movement of each shortingsheet relative to each other shorting sheet of the plurality of shortingsheets is prevented.
 11. The method of claim 8, wherein each of theshorting rings includes a center hole adapted to operatively connect toa rotation element; the method further comprising: operativelyconnecting a first rotation element to the center hole of the proximalshorting ring; operatively connecting a second rotation element to thecenter hole of the distal shorting ring; rotating at least one of thefirst and second rotation elements to skew the first and second shortingrings.
 12. The method of claim 11, wherein each of the center hole andthe rotation element are keyed to operatively connect to each other. 13.A lamination pack comprising: a lamination stack having a proximal faceand a distal face spaced apart from the proximal face; wherein thelamination stack: defines a slot therethrough extending from theproximal face to the distal face; defines a longitudinal axis; andincludes a plurality of laminations skewed relative to the longitudinalaxis; and a conductor bar including first and second bar ends and anintermediate portion intermediate the first and second bar ends;wherein: the intermediate portion of the conductor bar is disposedwithin the slot such that the first bar end extends from the proximalface and the second bar end extends from the distal face; theintermediate portion of the conductor bar is skewed relative to thelongitudinal axis; the first bar end is bent in a first radial directionrelative to the intermediate portion of the conductor bar; the secondbar end is bent in a second radial direction relative to theintermediate portion of the conductor bar; the first radial directionopposes the second radial direction; and the first and second bar endsexert a locking force on the lamination stack such that axial and radialmovement of each lamination relative to each other lamination of theplurality of laminations is prevented.
 14. The lamination pack of claim13, wherein: the plurality of laminations and the intermediate portionof the conductor bar are skewed to a skew angle relative to thelongitudinal axis; the bar end is bent to a locking angle relative tothe longitudinal axis; and the locking angle is greater than the skewangle.
 15. The lamination pack of claim 13, further comprising: aplurality of conductor bars; wherein each respective conductor bar ofthe plurality of conductor bars includes first and second bar ends andan intermediate portion intermediate the first and second bar ends;wherein: the intermediate portion of each respective conductor bar isdisposed within the slot such that the first bar end extends from theproximal face and the second bar end extends from the distal face; theintermediate portion of each respective conductor bar is skewed relativeto the longitudinal axis; the first bar end is bent in a first radialdirection relative to the intermediate portion of each respectiveconductor bar; the second bar end is bent in a second radial directionrelative to the intermediate portion of each respective conductor bar;the first radial direction opposes the second radial direction; and thefirst and second bar ends of each respective conductor bar exert alocking force on the lamination stack such that axial and radialmovement of each lamination relative to each other lamination of theplurality of laminations.
 16. The lamination pack of claim 13, furthercomprising: a proximal end ring disposed adjacent the proximal face; adistal end ring disposed adjacent the distal face; wherein: the firstbar end is electrically connected to the proximal end ring; and thesecond bar end is electrically connected to the distal end ring.
 17. Thelamination pack of claim 13, further comprising: a proximal end ringdisposed adjacent the proximal face; a distal end ring disposed adjacentthe distal face; wherein: the first bent bar end is disposed in a ringslot defined by the proximal end ring; and the second bent bar end isdisposed in a ring slot defined by the distal end ring.
 18. Thelamination pack of claim 13, further comprising: a shorting ringdisposed adjacent each of the proximal and distal faces; wherein: theshorting ring comprises a plurality of shorting sheets skewed relativeto the longitudinal axis by the locking angle to define a ring slot; andthe shorting ring defining a ring slot; wherein: the first bent bar endis disposed in the ring slot defined by the shorting ring disposedadjacent the proximal face; and the second bent bar end is disposed inthe ring slot defined by the shorting ring disposed adjacent the distalface.
 19. The lamination pack of claim 18, wherein: the first bent barend is exerts the locking force on the shorting ring disposed adjacentthe proximal face such that axial and radial movement of each shortingsheet relative to each other shorting sheet of the shorting ringdisposed adjacent the proximal face is prevented; and the second bentbar end is exerts the locking force on the shorting ring disposedadjacent the distal face such that axial and radial movement of eachshorting sheet relative to each other shorting sheet of the shortingring disposed adjacent the distal face is prevented.
 20. A method offorming a lamination pack, the method comprising: receiving a laminationstack onto a mandrel; attaching an adjustable retainer to the mandrel toretain the lamination stack on the mandrel; wherein the laminationstack: defines a proximal face and a distal face spaced apart from theproximal face; defines a longitudinal axis; includes a plurality oflaminations aligned radially relative to the longitudinal axis such thatthe plurality of laminations defines a plurality of slots extending fromthe proximal face to the distal face and distributed radially about aperiphery of the lamination stack; includes a plurality of conductorbars, wherein: each conductor bar includes first and second bar ends andan intermediate portion intermediate the first and second bar ends; andthe intermediate portion of each conductor bar is disposed within arespective one of the plurality of slots such that the first bar endextends from the proximal face and the second bar end extends from thedistal face; positioning a first shorting ring defining a plurality ofring slots adjacent the proximal face, such that the first bar end ofeach of the plurality of conductor bars is received into a respectiveone of the ring slots of the first shorting ring; positioning a secondshorting ring defining a plurality of ring slots adjacent the distalface, such that the second bar end of each of the plurality of conductorbars is received into a respective one of the ring slots of the secondshorting ring; skewing the first and second shorting rings in opposingradial directions to a skew angle relative to the longitudinal axis suchthat each of the plurality of conductor bars is skewed relative to thelongitudinal axis by the skew angle; adjusting the retainer to exert aretaining force on the lamination stack; wherein the retaining forceprevents axial movement and prevents radial rotation of each laminationrelative to each other lamination; incrementally skewing the first andsecond shorting rings in opposing radial directions to a locking anglerelative to the longitudinal axis such that the first and second barends are bent in opposing radial directions to a locking angle relativeto the longitudinal axis; wherein the retaining force is maintainedduring incremental skewing of the first and second shorting rings fromthe skew angle to the locking angle; and wherein the bent first andsecond bar ends exert a locking force on the lamination stack such thataxial and radial movement of each lamination relative to each otherlamination of the plurality of laminations is prevented.